Endodontic Instrument

ABSTRACT

A method of manufacturing endodontic instruments is disclosed. Each of the instruments includes a substantially non-cutting pilot portion, a relatively short working portion, and a flexible shank portion which is of a substantially smaller average circumferential span than the working portion. The working portion of one instrument may have a maximum circumferential span as that of the blank from which it is made. The instrument may be treated with either a surface treatment and/or a bulk treatment. The instrument may have a handle at its distal end for manual manipulation, or may be adapted for attachment to a mechanical handpiece. The non-cutting pilot, the short length of the working portion, and the flexibility of the shank combine to allow the instrument to be used in curved root canals without causing undue change in the natural root canal contours.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 60/732,367 entitled “Endodontic Instrument” filed Nov. 1,2005; U.S. Provisional Patent No. 60/732,047 entitled “EndodonticInstrument” filed Nov. 1, 2005; U.S. Provisional Patent Application No.60/732,631 entitled “Endodontic Instrument” filed Nov. 1, 2005; and U.S.Provisional Patent Application No. 60/732,039 entitled “TreatedEndodontic Instrument” filed Nov. 1, 2005 the entire contents of whichare incorporated by reference.

FIELD OF THE INVENTION

This invention relates to endodontic instruments for use in root canaldental procedures in general. More specifically, this invention relatesto a method for manufacturing endodontic instruments.

BACKGROUND OF THE INVENTION

Both circulatory and neural support for a tooth enters the tooth at theterminus of each root. During a root canal operation, any diseased pulptissue in the root canal is extracted using endodontic files and reamersthat are generally tapered. These instruments generally have workingportions along the major portions of the file. Since the root canals aresmall, curved and calcified, the instruments used have to withstand hightorsional stresses during such removal process so as not to complicatethe treatment by breaking.

The endodontic files and reamers used to clean out and shape the rootcanal are rotated and reciprocated in the canal by dentists, eithermanually or with the aid of dental handpieces onto which the files aremounted. Files of increasingly larger diameters are generally used insequence in order to achieve the desired cleaning and shaping.

Many endodontic instruments used for this operation have torsionallimitations. Some of the improved ones are disclosed in U.S. Pat. Nos.4,538,989, 5,464,362, 5,527,205, 5,628,674, 5,655,950, 5,762,497,5,762,541, 5,833,457, 5,941,760, and 6,293,795, the contents of theseare incorporated herein by reference. Some of these patents teachendodontic files made with an alloy of nickel/titanium containing morethan 40% titanium.

The files and reamers also have varying designs of cutting edges andsome of these designs are disclosed in U.S. Pat. Nos. 4,299,571,4,332,561, 4353698, 4,457,710, 4,661,061, 4,850,867, 4,904,185,5,035,617, 5,067,900, 5,083,923, 5,104,316, 5,275,562, 5,735,689,5,902,106, 5,938,440, 5,980,250, 6,293,794, and 6,419,488, 6,428,317,and Patent Application Publication Nos. US2002/0137008 A1, andUS2004/0023186 A1, incorporated herein by reference. Most of these fileshave working portions spanning the lengths of the shanks and includehelical cutting surfaces.

SUMMARY OF THE INVENTION

The present invention relates to a method of manufacturing an endodonticinstrument. The instrument includes a pilot portion at its proximal end,a relatively short working portion, and a flexible shank portion towardsits distal end, a portion of which is of a substantially smaller averagecircumferential span than the working portion. The working portion maybe towards the proximal end or towards the mid-portion of theinstrument.

According to one embodiment of the invention, the method formanufacturing includes:

providing a blank for making an instrument, said blank having acircumferential span,;

grinding said blank to form a non-working shank portion having aproximal end and a distal end, at least a portion of the shank having asubstantially smaller circumferential span than that of the blank;

forming a working portion extending not more than the length of thenon-working shank on said blank adjacent the distal end of thenon-working shank, and having a maximum circumferential spansubstantially corresponding to the circumferential span of the blank;

forming a pilot portion near one end of the blank close to the workingportion; and

treating at least a portion of the instrument including at least aportion of the shank portion, the working portion, the pilot portion orcombinations thereof.

In one embodiment, at least a portion towards the proximal end of thenon-working shank has substantially the same circumferential span asthat of the blank. In another embodiment, the entire length of the shankmay have a substantially smaller circumferential span than that of theblank. In a further embodiment, the shank may be tapered towards theproximal portion. In yet another embodiment, the shank may have aportion having a reduced circumferential span towards the proximal endto create a weak point.

The blank may also be treated prior to the grinding process. In oneembodiment, the blank may be treated at the manufacturing stage of theblank. In another embodiment, the blank may be treated after the blankmanufacturing process, but before the grinding process.

In one aspect, the treatment methods may include coating, sandblasting,anodizing, ion implantation, electro-polishing, etching or combinationsthereof, for modifying at least a portion of the working portion, and/orthe shank portion, and/or the pilot portion.

In another aspect, a blank may be subjected to heat setting, a cryogenictreatment, or combinations thereof.

In a further aspect, the instrument or blank may have a coating forimproving durability, and/or lubricity and/or improving cuttingefficiency and/or strength.

Some treatment methods may also impart a different color to the treatedportions. These colored portions may serve as length, depth or wearindicators.

The colored portion or section may remain on the un-ground portion. Forthe working portion, the un-ground portion may serve as a depth orlength indicator, or a wear indicator.

In one embodiment, the pilot portion may be a non-cutting portion. Inanother embodiment, the pilot portion may include abrasive surfaces. Inyet another embodiment, the pilot portion may be a continuous extensionof the working portion.

The present invention also relates to an endodontic instrumentincluding:

a relatively short working portion having a maximum circumferential spansubstantially corresponding to the circumferential span of a blank usedto make the instrument;

a pilot portion adjacent one end of the working portion; and

a flexible shank portion adjacent the other end of the working portion,a portion of which is of a substantially smaller average circumferentialspan than the working portion; wherein at least a portion of theinstrument including at least a portion of the shank portion, theworking portion, the pilot portion or combinations thereof has beentreated.

In one aspect, the blank is a treated blank. In another aspect, theouter surfaces of portions of the instrument have been treated. In afurther aspect, the instrument and /or blank may be coated.

The present invention further relates to a method of manufacturing a setof endodontic instruments having varying circumferential spans.

According to one embodiment of the invention, the method includes:

providing a set of blanks for making instruments, each having acircumferential span;

grinding each blank to generate a non-working shank having a proximalend and a distal end, at least a portion having a substantially smallercircumferential span than that of the blank;

forming a working portion adjacent to and extending not more than thelength of the non-working shank and having a maximum circumferentialspan substantially corresponding to the circumferential span of therespective blank;

forming a pilot portion near one end close to the working portion ofeach instrument; and

treating at least a portion of each of the instruments, said portionincluding at least a portion of the shank, the working portion, thepilot portion or combinations thereof.

In one aspect, at least a portion towards the proximal end hassubstantially the same circumferential span as that of the blank. Inanother aspect, the entire length of the shank may have a substantiallysmaller circumferential span than that of the blank. In a furtherembodiment, the shank may be tapered towards the proximal portion. Inyet another embodiment, the shank may have a portion having a reducedcircumferential span towards the proximal end to create a weak point.

According to another embodiment of the invention, the method includes:

providing a set of blanks for making instruments, each having anidentical circumferential span;

grinding each blank to generate a non-working shank having a proximalend and a distal end, at least a portion having a substantially smallercircumferential span than that of the blank;

forming a working portion adjacent to and extending not more than thelength of the non-working shank, one instrument in the set having amaximum circumferential span substantially corresponding to thecircumferential span of the blank;

forming a pilot portion near one end close to the working portion ofeach instrument.

In one embodiment, the shank portion of each of the instruments in theset is of substantially the same circumferential span which is smallerthan that of the blank. In another embodiment, only one instrument inthe set has at least a portion of the shank portion that is of thesubstantially the same circumferential span as that of the blank, andall the other ones have smaller circumferential span than the blank. Ina further embodiment, all instruments have at least a portion of theshank portion that is of substantially the same circumferential span asthat of the blank.

In one embodiment, at least a portion of each of the instruments,including at least a portion of the shank, the working portion, thepilot portion or combinations thereof, may be treated. In one aspect,the treatment methods may include coating, sandblasting, anodizing, ionimplantation, electro-polishing, etching or combinations thereof, formodifying the working portion, and/or the shank, and/or the pilotportion. In another aspect, a blank or instrument may be subjected toheat setting, cryogenic treatment, or combinations thereof.

As mentioned above, when a coated or treated blank is used, the treatedsurfaces or coating may be of a different color from the blank itself.The colored portion or section may remain on the un-ground portion. Forthe working portion, the un-ground portion may serve as a depth orlength indicator, or a wear indicator.

The blanks may also be treated prior to the grinding process, as noted.

According to a further embodiment of the invention, the method formanufacturing a set of endodontic instruments includes:

providing a set of groups of blanks for making a set of groups ofinstruments, each group of blanks includes a circumferential span, andeach group of blanks having a different circumferential span from anyother group of blanks;

grinding each blank to generate a non-working shank having a proximalend and a distal end, and each instrument made from the same group ofblanks has at least a portion of the shank having a substantiallysmaller circumferential span than that of the blank;

forming a working portion having a circumferential span, said workingportion adjacent to and extending not more than the length of thenon-working shank;

forming a pilot portion near one end of each blank close to the workingportion; wherein only the working portion of one instrument made fromeach group of blanks having a maximum circumferential span substantiallycorresponding to the circumferential span of each group of blanks.

In one embodiment, at least one of said instruments made from the samegroup of blanks has at least a portion towards the proximal end of theshank having substantially the same circumferential span as that of theblank. In another embodiment, the entire length of the shank portion ofall instruments made from the same group of blanks may have asubstantially smaller circumferential span than that of the blank.

The method may include a treating process, as noted above. In oneaspect, at least a portion of each of the instruments including theshank portion, the working portion, the pilot portion or combinationsthereof may be treated. In one embodiment, the treatment methods mayinclude coating, sandblasting, anodizing, ion implantation,electro-polishing, etching or combinations thereof, for modifying theworking portion. In another embodiment, a blank may be subjected to heatsetting, cryogenic treatment, or combinations thereof. For the coated ortreated blank, as mentioned above, the treated surfaces or coating maybe of a different color from the blank itself. The colored portion orsection may remain on the un-ground portion. For the working portion,the un-ground portion may serve as a depth or length indicator, or awear indicator.

In another aspect, the blanks may be treated prior to the grindingprocess, as also noted above.

In one embodiment, a series of two instruments may be made from onegroup of blanks having identical circumferential span even though onlyone of the instruments has a working portion having the samecircumferential span as the blank. In another embodiment, a series ofthree instruments may be made from a group of blanks having identicalcircumferential span even though only one of the instruments has aworking portion having the same circumferential span as the blank. Inother embodiments, more than three instruments may be made from a groupof blanks having identical circumferential span even though only one ofthe instruments has a working portion having the same circumferentialspan as the blank.

In one embodiment, the number of group is equal to one.

The present invention still further relates to a set of groups ofendodontic instruments made from a set of groups of blanks, each groupincluding an instrument having:

a relatively short working portion having at least one working surfacehaving a maximum circumferential span;

a pilot portion; and

a flexible shank portion adjacent the working portion, a portion ofwhich is of a substantially smaller average circumferential span thanthe working portion; wherein only one instrument in each group has amaximum circumferential span substantially corresponding to thecircumferential span of each group of blanks.

In one aspect, at least a portion of each of the instruments includingthe shank, the working portion, the pilot portion or combinationsthereof may be treated.

In another aspect, at least one instrument made from each group ofblanks has a portion towards the proximal end of the shank portionhaving substantially the same circumferential span as that of the blank.

In a further aspect, the short working portion extends not more than thelength of the non-working shank portion.

In one embodiment, the instrument may have a handle at its distal endfor manual manipulation. In another embodiment, instrument may have ahandle at its distal end that is adapted for attachment to a mechanicalhandpiece, including a rotary handpiece. At least a portion of the endattaching to the handle portion is treated. The treatment may improvethe attachment strength and minimize separation of the shank portionfrom the handle portion.

The substantially non-cutting pilot, the short length of the workingportion, and the flexibility of the shank portion combine to allow theinstrument to be used in curved root canals without causing undue changein the natural root canal contours.

The blank may have a substantially circular, a substantiallyrectangular, a substantially triangular, or a substantially ellipticalcross-section.

The working surfaces may be helical; may have edges forming a continuouscurve; may have edges twisting not more than 359° about the longitudinalaxis; may have curved cutting edges about the longitudinal axis; mayhave straight cutting edges along the longitudinal axis; may havestraight cutting edges at an oblique angle from the longitudinal axis;may have cutting edges having projections that are non-intersecting witheach other or the longitudinal axis; or combinations thereof.

In one embodiment, the pilot portion may be about the same length as theworking portion. In another embodiment the pilot portion may be anextension at the end of the working portion.

While the working portion and the pilot portion may be formed bygrinding, as described above, they may also be formed by casting ormolding.

The present invention together with the above and other advantages maybest be understood from the following detailed description of theembodiments of the invention illustrated in the drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art endodontic instrument;

FIGS. 2 and 2 a each shows an embodiment of an endodontic instrumentmade with methods according to the present invention;

FIGS. 3, 3 a and 3 b each shows another embodiment of an endodonticinstrument made with methods according to the present invention;

FIGS. 4, 4 a 1, 4 a, 4 b, 4 c, 4 c 1, 4 d, 4 e, 4 e 1, and 4 f eachshows a further embodiment of an endodontic instrument made with methodsaccording to the present invention;

FIG. 5 shows a schematic block diagram depicting an exemplary methodaccording to the present invention for making an endodontic instrument

FIG. 6 shows an exemplary equipment used in the manufacturing process ofthe present invention;

FIG. 7 shows an exemplary endodontic instrument of the present inventionhaving a handle;

FIG. 7 a and 7 b show an exemplary endodontic instruments of the presentinvention having rotary handles;

FIGS. 8 a, 8 b and 8 c each illustrates a series of endodonticinstruments of the present invention having different maximumcircumferential spans or diameters of the working portion; and

FIG. 9 and 9 a each shows another embodiment of an endodontic instrumentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of the presently exemplifiedembodiments of dental instruments or tools in accordance with thepresent invention, and is not intended to represent the only forms inwhich the present invention may be constructed or utilized. Thedescription sets forth the features and the process for constructing andusing the dental tools or instruments of the present invention inconnection with the illustrated embodiments. It is to be understood,however, that the same or equivalent functions and structures may beaccomplished by different embodiments that are also intended to beencompassed within the spirit and scope of the invention.

An endodontic instrument in accordance with the present invention may beused in a root canal procedure. Some exemplary configurations may befound in U.S. Pat. No. 4,850,867, the content of which is incorporatedherein by reference.

Traditional instruments typically include long, tapered working portions22 having helical flutes along the entire length of the working portion22, such as shown in FIG. 1. These instruments are typically made bygrinding a cylindrical wire. Such long working portions also mean morecontact area between the root canal and the instrument, thus subjectingthe instrument to higher torsional forces during operation.

An endodontic instrument 12 of the present invention has a relativelyshort working portion 22, as exemplified in FIG. 2, 2 a, 3, 3 a, 3 b, 4,4 a 1, 4 b, 4 c, 4 c 1, 4 d, 4 e, 4 e 1, or 4 f, leading to smallerareas of contact with the root canal. The smaller contact areas mayresult in lower torsional forces on the instrument 12 during use. Theshorter working portion 22 also may provide the dentist withsubstantially improved control over where cutting of dentin occurs andtherefore causes much less unintended cutting of dentin and change ofthe natural curvature.

In the present invention, a blank 30 of a substantially circular, asubstantially square, a substantially rectangular, a substantiallytriangular, or a substantially elliptical cross-section may be ground toform an endodontic instrument 12, as exemplified in FIGS. 2, 2 a, 3, 3 aand 3 b.

The present invention includes an instrument 12 having a shank portion16 that has a substantially smaller circumferential span or diameter forthe major portion of its length than a traditional instrument. A smallcircumferential span or diameter leads to a more flexible instrument.This flexibility allows the instrument 12 to follow the curve of a canalmore easily.

The shank portion 16 is also longer than the working portion 22. Atraditional instrument, by contrast, has a very short shank portion 16,if any. The length of the shank portion 16 provides for an instrument 12that may bend more readily as it encounters any change in direction inthe channel of the tooth.

The instrument 12 also has a substantially non-cutting pilot portion 10.The pilot portion 10, the short length of the working portion 22, inaddition to the length and flexibility of the shank 16, all combine tofurther allow the instrument 12 of the present invention to more easilyfollow the natural curvature of the entire root canal without causingundue change in the natural root canal contours. It also opens up morechoices for materials that may be suitable for constructing theinstrument 12, including materials that may not be suitable fortraditional instruments, materials that are not traditionally consideredas having high degrees of flexibility, or materials having improvedstrength. Such improvements may be introduced through treatments such ascryogenic treatments, heat setting or combinations thereof.

Such treatments for improved strength, which may introduced acorrespondingly undesirable loss in flexibility of the blank sometimes,may still generate blanks that are suitable for the present inventionbecause of the configuration of the instrument of the present invention.

The blank 30 may include a titanium alloy such as nickel-titanium alloy,titanium-nitride alloy, titanium-aluminum-vanadium alloys or similar;stainless steel; silver and silver alloys; aluminum; any amorphousmetals; or a similar metal that is amenable to being drawn into a blank30 of small diameter or circumferential span or a wire-like form. For atitanium alloy, the amount of titanium may be present at, for example,at least about 25% by weight, more for example, may be present at, forexample, at least about 50% by weight. The nickel-titanium alloys mayalso include impurities such as C, O, N, Co, Cr, Zr, Hf, Nb, Pt, Pd, V,Fe or mixtures thereof. Fe may also strengthen and improve ductility ofthe alloy. These blanks 30 may be made into endodontic instruments 12having good torsional resistance and good flexibility.

A suitable non-metal may also be used and may include a polymeric alloysuch as ULTEM®, which is an amorphous thermoplastic polyetherimide,Xenoy® resin, which is a composite of polycarbonate andpolybutyleneterephthalate, Lexan® plastic, which is a copolymer ofpolycarbonate and isophthalate terephthalate resorcinol resin (allavailable from GE Plastics); liquid crystal polymers, such as anaromatic polyester or an aromatic polyester amide containing, as aconstituent, at least one compound selected from the group consisting ofan aromatic hydroxycarboxylic acid (such as hydroxybenzoate (rigidmonomer), hydroxynaphthoate (flexible monomer), an aromatic hydroxyamineand an aromatic diamine, (exemplified in U.S. Pat. Nos. 6,242,063,6,274,242, 6,643,552 and 6,797,198, the contents of which areincorporated herein by reference), polyesterimide anhydrides withterminal anhydride group or lateral anhydrides (exemplified in U.S. Pat.No. 6,730,377, the content of which is incorporated herein byreference); any or combinations thereof.

The blank 30 may be present in a continuous spool. When the blank 30 isin a spool, it may undergo a straightening process prior to being cutand/or ground. For a blank 30 of nickel-titanium alloy, thestraightening process is not needed as the winding process does notimpart a permanent memory to the blank 30.

In one embodiment, the blank 30 may be cut into the needed dimensionprior to feeding the blank 30 through the grinding process. In anotherembodiment, the blank 30 may be fed through the grinding process priorto being cut into the required dimension.

An instrument 12 typically has a length of about 30 mm (1.2 inches), andhas a proximal end adapted to be mounted to a conventional handle 25, asshown in FIG. 7 or to rotary handles 25, as shown in FIGS. 7 a and 7 b.The conventional handle 25 may be adapted for manual cutting of the rootcanal. The rotary handles 25 may be adapted for mounting to a mechanicalhandpiece, such as a rotary handpiece or vibratory handpiece. The shankportion 16 may be cylindrical, as shown in FIGS. 2 and 3, or may be ofany other cross-section mentioned above, and may have a circumferentialspan or diameter of between about 0.2 to about 0.8 mm (0.01 and 0.03inches). The working portion 22 may have a length of about 0.5 mm (0.02inches, or up to about 14 mm (0.5 inches). In one embodiment, theworking portion 22 may be cylindrical. In another embodiment, theworking portion 22 may be ground to be slightly tapered towards thepilot portion 10. In a further embodiment, the working portion 22 may beground to be slightly tapered towards the shank portion 16. In yetanother embodiment, the working portion 22 may be ground to be slightlytapered towards both the pilot end 10 and the shank portion 16, asshown, for example, in FIGS. 2, 2 a, 3, 3 a, 3 b, 4, 4 a, 4 b, 4 c, 4 d,4 e, 8 a, 8 b and 8 c. Any or all of these illustrates embodiments of anendodontic instrument 12 which may be fabricated in accordance with thepresent invention.

The working portion 22 of the instrument 12 may be flat, orsubstantially in one plane, and having a thickness as shown in FIGS. 3,3 a, 4 and 5. In one embodiment, the flattened working portion 22 mayvary in thickness, from the thinner edge to a thicker central portion.In another embodiment, the thickness of the working portion 22 may besubstantially uniform. In another embodiment, the working portion 22 mayhave projections that are out of plane or may be of a wedge-like sectionor projections 18 that are not helically wound with respect to thelongitudinal axis of the shank 16, as exemplified in FIGS. 2 a, 2 d 3, 3a, and 4. The projecting sections 18 extend beyond radius R of the shank16, as measured perpendicular to the longitudinal axis. One or more ofthese projections 18 may be straight, radiating outward about theworking portion 22 in one plane, as shown in FIG. 2 a.

Referring to FIGS. 2 and 2 a, the working portion 22 may have asubstantially circular cross-section. As shown, the working portion 22may also have a slight taper present at both ends of the working portion20 and 24, as shown. The tapering makes the largest diameter portion nottowards either one of the ends 20 and 24, but either about themid-section of the working portion 22, or just off the mid-section ofthe working portion 22, as shown in FIGS. 2, 2 a, 3, 3 a, 3 b, 4, 4 a, 4b, 4 c, 4 e and 4 f.

The working portion 22 may also be suitably tapered in three portions. Afirst transition portion 20 increases in diameter from the distal end ofthe pilot portion 10 until it meets the main body of the working portion22. The main body portion also increases in diameter towards its distalend 24, but may be at a lesser angle than the first transition portion20, or vice versa. The main body of the working portion 22 connects atits distal end to a second transition portion 24 which decreases indiameter from its proximal end to its distal end, where the secondtransition portion 24 connects to the shank portion 16. Otherembodiments are possible, including a reverse taper whereby the proximalend diameter of the working portion 22 may be greater than the distalend diameter, or any other combination.

In the embodiments as exemplified in FIGS. 2, 2 a, 3, 3 a, 3 b, 4, 4 a,4 b, 4 c, 4 e and 4 f, the non-working shank 16 is of a substantiallycylindrical shape and has a proximal end 16 a and a distal end 16 b. Inother embodiments, shanks 16 having other cross-sectional shapes, suchas a triangle, a square or a rectangle, may also be contemplated.

The tapered end 24 of the working portion 22 is contiguous with thedistal end 16 b of the non-working shank 16. In one embodiment, thetapered end 24 may be tapered such that at the point of joining with thedistal end 16 b of the non-working shank 16, there is a matching ofdiameters. In another embodiment, the distal end 16 b is of a slightlylarger diameter than the narrow portion of the non-working shank 16 sothat there is a smooth transition from the tapered end 24 of the workingportion 22 towards the non-working shank 16. This is shown in FIG. 9,and will be discussed further below. In a further embodiment, theproximal end of the non-working shank 16 may have a slightly largerdiameter than the rest of the non-working shank 16.

In the embodiments as shown in FIGS. 2 and 2 a, the outer peripheral ofthe working portion 22 includes at least two spiral or helical workingsurfaces 18 (as shown in FIG. 2), or the surfaces 18 may form at leasttwo continuous curves (as are shown in FIG. 2 a). In other embodiments,the working portion 22 may have one helical working surface 18, or onecontinuous curve.

In some embodiments, the working portion 22 may be flattened and/orotherwise shaped to alter its cross-sectional geometry. In oneembodiment, the working portion 22 may be flatted to an extent that thecross-section is an ellipse. In another embodiment, the working portion22 may be flattened substantially so the cross-section resembles aflattened quadrilateral.

The at least two spiral or helical working surfaces 18 may be formedprior to flattening the working portion 22, which may result in asubstantially spiral or helical structure(s) 18 that may includesignificant working surfaces that may contact the work space on theapical portions of the longest dimension of the cross section of workingportion 22.

Other embodiments of the working portion having other configurations ofthe working surfaces 18 are described in FIG. 3, 3 a, 3 b, 4, 4 a, 4 b,4 c, 4 d, 4 e, and 4 f.

FIGS. 3, 3 a and 3 b show an instrument having curved working or cuttingsurfaces or edges 18 along the outer peripheral of the working portion22. These curved edges 18 may twist or curve not more than 359° aboutthe longitudinal axis of the shank portion 16, such as exemplified inFIG. 4.

In another embodiment, the working surfaces or edges 18 may be straight,either along the longitudinal axis of the working portion 16, or at anoblique angle, as shown in FIGS. 4 and 4 a. The straight cutting edgesor surfaces 18 may extend substantially along the length of the workingportion in one continuous edge, as are also shown in FIGS. 4 and 4 a. Inother embodiments, each of the straight cutting edges may be in severalsections, as shown in FIGS. 4 b and 4 c. FIG. 4 a 1 and 4 c 1 clearlyshow the working or cutting surfaces 18 of the embodiments 4 a and 4 c,when viewed straight on from the pilot portion 10.

In the embodiments as shown in FIGS. 4, 4 a, 4 b and 4 c, thecross-section of the working portion may be of a substantiallyrectangular shape. If the cross-section is substantially circular, thelongitudinally straight or oblique edges may follow the curved portionsof the working portion, but still in substantially straight or obliquefashion.

The working portion 22 may also be flattened, rather than cylindrical.One exemplary embodiment is shown in FIG. 4 d. In a flattened workingportion 22, the two outer edges 18 and the front edges would normally dothe cutting. The cross section of such a working portion 22 would be arelatively thin rectangle.

In another embodiment, the flattened working portion 22 may include atleast one projecting section 18, each projecting section extendingtowards the pilot portion 10, the projecting section 18 including aleading portion extending forward of the portion having a maximumcircumferential span and making an angle with the longitudinal axis ofthe shank 16 of less than about 90° and a trailing edge portionextending rearward of the portion having a maximum circumferential spanand making an angle of less than about 90° with the same longitudinalaxis, each projecting section does not twist about the longitudinal axisof the working portion more than 359° about the longitudinal axis, asexemplified in FIG. 4 e, or the cross-sectional view in FIG. 4 e 1; orthe projections 18 that are non-intersecting with each other or thelongitudinal axis, as exemplified in FIG. 4 f.

Of the two portions of the non-working shank 16, the portion towards theproximal end 16 a may be of a larger or smaller circumferential span,for example, diameter, than the portion towards the distal end 16 b. Inone embodiment, the proximal portion 16 a and distal portion 16 b may beground so that the proximal portion 16 a may be of a smaller, forexample, diameter than the largest diameter portion of the workingportion 22, such as shown in FIG. 9. In another embodiment, only thedistal portion 16 b may be ground so that the proximal portion is ofapproximately the same diameter as the largest diameter working portion22, such as exemplified in FIG. 8 b. In a further embodiment, the shank16 may be ground in such a way that the distal end 16 b transitionssmoothly form the distal end 24 of the working portion 22 and taperstowards the proximal end 16 a, as shown in FIG. 9. In yet a furtherembodiment, the shank 16 may be ground to have a portion 16 c having areduced circumferential span or diameter, as shown in FIG. 9 a. Thenon-working shank 16 may generally be solid.

The tip of an instrument 12 in accordance with the present invention maybe formed with a substantially non-cutting pilot portion 10, while moststandard instruments have a cutting tip. The configuration of the shank16 of the present invention may also be ground to provide more flexibleshanks 16 than in comparable standard instruments 12, as noted before.In general, the shank portion 16 may also be substantially longer thanthe working portion 22, providing for a working portion 22 that may bendas it encounters any change in direction in the channel of the tooth, tomore easily follow the curve of a canal. The substantially non-cuttingpilot portion 10, the short length of the working portion 22, and theflexibility of the shank 16, all combine to allow the instrument of thepresent invention to more easily follow the natural curvature of theentire root canal without causing undue change in the natural root canalcontours. The shorter cutting lengths also may provide the dentist withsubstantially improved control over where cutting of dentin occurs andtherefore causes much less unintended cutting of dentin and change ofthe natural curvature.

The substantially non-cutting pilot portion 10 may have a diameter smallenough to allow an instrument 12 to enter the apical area of the rootcanal of a human tooth and to act as a guide to follow the canal to theapex. Thus, the purpose of the pilot portion 10 is to guide theinstrument 12, and not necessarily to perform any cutting. In oneembodiment, the pilot portion 10 may be a non-cutting portion. In someembodiments, the substantially non-cutting portion 10 may include anabrasive surface. The abrasive surface may be imparted through coating,sandblasting, anodizing, ion implantation, etching, electro-polishing orcombinations thereof, as further discussed below. In still otherembodiments, the pilot portion 10 may have raised edges or otherprojections on its surface, as long as they do not cause the pilotportion 10 to have a substantial cutting effect.

The pilot portion 10 may be, for example, between about 0.01 and 14 mmlong, more for example between about 0.75 and 3 mm. The working portion22 may be, for example, between about 0.5 and 14 mm long, more forexample, between about 0.5 and 4.0 mm long.

The pilot portion 10 and working portion 22 may both be tapered ornontapered. If tapering is used in the pilot portion 10, it may usuallyincrease in diameter from its proximal end to its distal end.

The shank 16 may generally have a constant diameter, but may also betapered, as noted before.

In FIG. 3, the pilot portion 10 is a short portion extending from theend 20 of the working portion 22. As shown, the pilot portion 10 is asmooth tapered cylinder with a blunt proximal end. In other embodiments,the pilot portion 10 may have rounded (bullet shaped) ends, asexemplified in FIG. 3 a, where it is present as a slight extension or astump at the end 20 of the working portion 22. This may be rounded, andmay be generated by grounding or polishing the working end 20.

In FIG. 3 b, the pilot portion 10 is almost of the same length as thatof the working portion 22. In this configuration, the instrument 12 maybe useful a coronal shaper. In FIGS. 3 and 3 b, the pilot portion 10 asshown is also a smooth cylinder having a uniform circumferential span,for example, diameter, along its length, except for the end. In otherembodiments, the pilot portion 10 may be tapered towards the end. Asshown, the end of FIGS. 3 and 3 b are not rounded. In other embodiments,the end may be rounded, such as shown in FIG. 3 a, as noted before.

One embodiment of an exemplary process for making an instrument 12, isshown schematically in FIG. 5, In FIG. 5, a blank 30 having a diametercorresponding to the maximum diameter of the working portion 22 may befed through a grinding apparatus, such as that exemplified in FIG. 6, tobe described below. Some details of this apparatus may also be found inU.S. Pat. No. 5,464,362, the content of which is incorporated herein byreference.

The exemplary process includes:

providing a blank 30 having a length and a circumferential span inprocess 1;

grinding the blank 30 to form a non-working shank 16 having a proximalend 16 a and a distal end 16 b, at least a portion towards the proximalend 16 a having substantially the same circumferential span as that ofthe blank 30, and at least a portion towards the distal end 16 b havinga substantially smaller circumferential span than that of the blank 30in process 2;

forming a working portion 22 having at least one working surface 18,said working portion extending not more than the length of thenon-working shank 16 on said blank 30, and having a maximumcircumferential span substantially corresponding to the circumferentialspan of the blank 30 in process 3; and

forming a pilot portion 10 near one end of the instrument 12 close tothe working portion 22 in process 4.

In another embodiment, the processes may be performed in any order.These processes may be carried out using an apparatus as exemplified inFIG. 6, described below.

The process may include treating at least a portion of the instrument 12including at least a portion of the shank 16, the working portion 22,the pilot portion 10 or combinations thereof. The treatment process maybe carried out prior to or after the grinding the grinding process, asshown in dotted line in FIG. 5. The treatment process may also berepeated.

As noted above, FIG. 6 schematically illustrates an exemplary machiningapparatus for practicing the method of the present invention. Thegrinding process itself may be any known process, such as that describedin U.S. Pat. No. 5,464,362, also noted above.

An instrument 12 may be made from a blank 30 having, for example, adiameter that is substantially equal to the largest diameter of theworking portion 22. Blanks 30 with other cross-sectional configurationmay be used, as discussed above. In accordance with an illustratedembodiment of the present invention, the blank 30 may be in a continuousspool, as noted above, and may be positioned to extend through an axialfeed block 32 and an indexing block 34 as shown in FIG. 6. A holdingfixture 36 is positioned to support the forward end of the blank 30adjacent the periphery of a rotating grinding wheel 38.

In the embodiment as shown in FIG. 6, the blocks 32, 34 may be advancedso that the blank 30 may move axially past the rotating grinding wheel36 at a speed of, for example, between about 3 to 8 inches per minute(75 mm to about 200 mm), and more for example, of not more than about 5inches (about 125 mm) per minute, if a blank of nickel-titanium is used.In other embodiments, higher rotation rates may be used. Concurrentlywith this axial movement, the indexing block 34 may also slowly rotatethe blank about its axis at a controlled speed, so that the groundsurface of the working portion 16 may have a helical configuration asdescribed above with respect to FIGS. 2 and 2 a, if desired. In otherembodiments, the indexing block may be stationary, or it may have aslight translational movement for generating working surfaces havingother configurations, such as those as shown in FIGS. 3, 3 a, 3 b, 4, 4a, 4 b, 4 c, 4 d, 4 e and 4 f.

The blank 30 may move past the wheel once or more than once for eachground surface, and thus the blank 30 may be positioned with respect tothe wheel 38 such that the full depth of the cut is removed in a singlepass or multiple passes, respectively.

The grinding wheel 38 may be rotated at a relatively slow surface speedof, for example, not more than about 3000 feet per minute, and more forexample, not more than about 2200 feet per minute. Further, the wheel 38may be composed of a relatively fine grit, which is greater than, forexample, about 200 grits, and more for example, about 220 grits. Thewheel 38 having the above grit sizes may be fabricated from siliconcarbide. In other embodiments, diamond particles may also be used as thegrinding surfaces.

The grinding wheel 38 may also be rotated at higher surface speeds. Atthe higher speeds, more than one pass may be employed.

The wheel 38 may be oriented to rotate about an axis generally parallelto the axis of the advancing blank 30 to form a working surface 18, forexample, as shown in FIGS. 2 and 2 a. For a slow rotating speed, ahelical configuration may be achieved. If a tapered working portion 22is desired, the axis of the index block 34 may be slightly inclined withrespect to the rotational axis of the wheel 38, so as to provide acontrolled and variable depth of cut along the working portion 22.

When the blank 30 has advanced past the rotating wheel 38 a distancesufficient to form the first working surface along the desired workingportion 22 on the instrument 12, the table 39 supporting the feed block32, the index block 34, and the fixture 36 may be moved laterally, thenaxially rearwardly, and then laterally back to its original position,while the blank 30 is concurrently rotatably indexed about its axis. Theangular extent of this indexing will depend upon the number of workingsurfaces 18 desired on the finished instrument. For example, if threeworking surfaces 18 are to be formed on the working portion 22, theblank 30 may be indexed 1200. After forming the first working surface18, the blank 30 may then again be axially advanced while being slowlyrotated, and so as to form a second surface, and so on, if desired. Thetable 39 is then again moved laterally and rearwardly in the mannerdescribed above, and the blank 30 is rotatably indexed another 120°. Thegrinding process is repeated to form the third surface of the instrument12.

If an instrument 12 has two working surfaces 18, the blank 30 is indexed180° between the two machining operations.

After forming the working surfaces, the blank 30 may be ground to asmaller diameter to form a non-working shank 16 but leaving the blank 30in its original diameter towards the proximal portion 16 a prior tobeing severed by such methods, for example, by axially advancing theblank 30 and then moving the grinding wheel 38 laterally through theblank 30. For example, only the distal portion 16 b may be ground sothat the proximal portion is of approximately the same diameter as thelargest diameter working portion 22, such as exemplified in FIG. 8 b. Inanother embodiment, the shank 16 may be ground in such a way that thedistal end 16 b transitions smoothly from the distal end 24 of theworking portion 22 and tapers towards the proximal end 16 a, as shown inFIG. 9. In yet a further embodiment, the shank 16 may be ground to havea portion 16 c having a reduced circumferential span or diameter, asshown in FIG. 9 a. The grinding may be taken in any order other than asillustrated above, if other configurations of the working surfaces aredesired.

The severed blank/instrument 12 may then be further treated. Thetreatment process may include coating, sandblasting, anodizing, ionimplantation, etching, electro-polishing, heat setting, cryogenictreatment, or combinations thereof. The treatments including coating,sandblasting, anodizing, ion implantation, electro-polishing, etching orcombinations thereof, may be performed to modify the surfaces of atleast a portion of the working portion 22, and/or the shank 16, and/orthe pilot portion 10. The treatment may also act to remove any burrsthat may form during the grinding process.

In addition, the surface treatments may also remove any oxidizedmaterial, for example, an oxide layer that may be present on the surfaceof the blank 30 that is generated during the manufacturing process ofthe blank 30. The oxidized layer may be regenerated even after thetreatment, but not to the same extent as the untreated surfaces. Theremoval of the oxidized layer may also improve the cutting efficiency ofthe working portion 22.

In another embodiment, after the treatment, or as the treatment process,a coating may be formed on the surface. This coating may, on the onehand, minimize the re-forming of the oxidized layer, while at the sametime provide friction reduction and/or durability enhancement, asdiscussed further below.

In a further embodiment, the existence of the oxide layer may beadvantageous in improving corrosion resistance, durability and/orfinishing of the surface. An oxide layer of titanium may, for example,impart coloring to the surface based on the thickness of the layer andmay be utilized as a wear or depth indicator. Oxide layers thicker thanan untreated passivation layer may also impart increased corrosionresistance and durability as many metal oxides are extremely hard andthicker layers may be less prone to wearing that may expose the metalsurface and lead to corrosion. Increasing the thickness of the oxidelayer may also be useful in preserving the layer when exposed toenvironments where oxygen is not available to regenerate the layer.

If a flattened working portion 22 is desired, as shown in FIGS. 4 d, 4 eand 4 f, a flattened blank 30 may be used to generate an entireflattened instrument 12. The feed block 32, the index block 34 and thefixture 36 may be modified and adapted for such a blank 30. In anotherembodiment, a non-flattened blank 30 may be used, an additionalcompression process may be implemented to form the flattened workingportion 22. In yet another embodiment, a non-flattened blank 30 may beused and the flattened working portion 22 may be formed by grinding.

In one embodiment, the flattened working portion may vary in thickness,from a thinner edge to a thicker central portion. In another embodiment,the thickness of the working portion may be substantially uniform.

The instrument 12 may also undergo cryogenic treatment, heat setting,combinations thereof, or others, provided that any or combinations ofthese treatments do not adversely affect the surface properties impartedby the surface treatments, if any of these treatments is previouslyperformed on the instrument.

In another embodiment, the process of fabricating an instrument using atreated blank is disclosed, as is also shown in FIG. 5, in dotted lines.

The treatment may include coating, sandblasting, anodizing, ionimplantation, electro-polishing, etching, or combinations thereof, asdisclosed above. Any or combinations of these treatments may serve tomodify the surface properties of the instruments, as disclosed above.Other treatments, including cryogenic treatment, heat setting orcombinations thereof, may serve to improve the bulk properties, forexample, the strength of the metal, polymer or alloy, by, for example,modifying the molecular structure of the base material. These may alsobe used in combination with the surface treatments mentioned above,either before or after any of the other treatments, provided that onetype of treatment does not adversely change or affect the desirableeffects imparted by another type of treatment, as noted. In general, theproperties least likely to be affected by other treatment methods areperformed first.

A suitable cryogenic treatment is described in U.S. Pat. No. 6,314,743,the content of which is incorporated herein by reference. An exemplarytreatment may involve a cryogenic cycle having a cool down phase from aninitial start time, during which the blank 30 may be cooled down in adry cryogenic environment to about −300° F., over a span of betweenabout six (6) and eight (8) hours, followed by a cryogenic hold phaseduring which the blank 30 may be held at about −300° F. over betweenabout twenty-four (24) and thirty-six (36) hours, followed by acryogenic ramp up phase during which the blanks 30 are ramped up toabout −100° F. over between about six (6) and eight (8) hours. Then afirst tempering cycle having a ramp up phase may be performed, duringwhich stage the blank is ramped up in a dry tempering environment toabout 350° F. over about one-half (½) hour, followed by a hold phaseduring which the blank 30 may be held at about 350° F. over about two(2) hours, followed by a ramp down phase to below about 120° F., but notgenerally all the way to the ambient temperature, over between about two(2) and three-and-half (3½) hours. A second tempering cycle may followwhich may have a time-temperature profile fairly comparable to the firsttempering cycle. In some methods, a third tempering cycle may beperformed.

The cryogenic ramp down phase may be arranged to have a varying rate ofdescent. For example, the descent may be steeper initially from ambientto about −100° F. and then more gradual thereafter for temperaturesbelow −100° F. to about the cryogenic hold temperature of about −300° F.The temperature descent from the start time at ambient temperature tothe about −100° F. level may be achieved over about the first one (1)hour after the start time, while the temperature descent from belowabout −100° F. to about −300° F. may be achieved over between about five(5) and seven (7) hours.

The cryogenic ramp up phase may also have a varying rate of ascent, forexample, that may correspond to an exponential decay of the cryogenichold temperature from the about −300° F. to about −100° F. over betweenthe about six (6) and eight (8) hours. The exponential decay of thecryogenic hold temperature from the about −300° F. to about −100° F. mayalso include a stage when a temperature of about −200° F. is not reachedfrom the base hold temperature of −300° F. until six (6) hours into thecryogenic ramp up phase, while the remaining decay up to −100° F. occursover a next two (2) hours. In other embodiments, the exponential decayof the cryogenic hold temperature from the about −300° F. to about −100°F. may be arranged to transpire such that a temperature of about −200°F. is not reached from the base hold temperature of −300° F. untilfive-and-a-half (5½) hours into the cryogenic ramp up phase, theremaining decay up to −100° F. occurring over a half (½) hour period.

In an exemplary embodiment, the cryogenic environment may be provided bya Dewar chamber and the tempering environment may be provided by aconvection oven. Accordingly, the transition between the cryogenic cycleand the first tempering cycle would entail physical transfer of theblank from Dewar chamber to the convection oven.

Typically, a hold down phase at about −300° F. may extend between abouttwenty-four (24) and thirty-six (36) hours. During this “hold phase” theblank 30 may thermally contract. If the blank 30 is made of metal or ametallic alloy, it is surmised that the microstructure re-organizesitself to become more spatially uniform. This uniformity may providestronger blanks for making the instruments by decreasing the packingdensity defects.

Another cryogenic process is disclosed in U.S. Pat. No. 6,332,325,incorporated herein by reference. The process subjects an article ofmanufacture to extreme negative temperatures and cycling the articlebetween a set of negative temperatures for a number of cycles. Theprocess is completed by heating the article to an extreme positivetemperature and then allowed to cool to ambient room temperature. It isshown that this cryogenic thermal cycling process strengthens thearticle by realigning its molecular structure to eliminatemicro-cracking and other manufacturing deforming characteristics.

Other cryogenic treatment methods may be found, for example, U.S. Pat.No. 4,482,005 (Voorhees), or U.S. Pat. No. 5,259,200 (Nu-Bit, Inc.), thecontent of which is incorporated herein by reference. The Voorheespatent discloses a cryogenic cycle having ramp down and ramp up phasesflanking a wet or immersion “soaking” phase. The Voorhees discloses thatfor “tool steel”, the wet process produces an instrument with longerlasting sharpness. The Nu-Bit patent discloses a quenching process byessentially dropping a target into a liquid nitrogen bath, and let setthere for the ten (10) minutes or soon, sufficient time for the liquidnitrogen to boil away. After the bath, the instrument is brought back toroom temperature by a jet stream of room-temperature air, making theentire process a forty minute start to finish (including the 10 minutebath) process. This quick dip method reports a gain of up to a fiftyfold (50×) improvement in drill bits. Both of these methods may have tobe modified to be practiced for blanks 30 used to make fine instruments12 like endodontic files.

The cryogenic treatment may be amenable to blanks 30 after they havebeen manufactured, for example, after they have been drawn into the formof blanks 30, other treatment process may also be amenable to beperformed during, for example, the extrusion or drawing process. Forexample, heat treatments or varying drawing speeds may be used to modifythe properties of the blanks 30, for example, to strengthen the blanks30, during their manufacturing process. For heat setting treatments, acycling between hot and cold may be employed. The rate of the heatingand cooling cycles may also be varied. Other thermal treatments mayinclude localized laser treatment. By varying the aging temperature, thedrawing or extrusion rates, the rate of heating and cooling cycles, anyirregularities in the molecular structure or molecular packing may bemodified. Multiple incremental drawing or deformation may also result inbetter uniformity and better properties than single drawing process.

Some examples of these processes may be found in U.S. Pat. Nos.4,704,329, and 6,332,325, the contents of which are incorporated hereinby reference.

While some of these treatment methods may be more amenable to blanks 30than instruments 12, they may be used for instruments 12 also, with somemodifications. For example, the method discussed in U.S. Pat. No.6,332,325 may be used to strengthen the blank 30 by realigning itsmolecular structure to eliminate micro-cracking and other manufacturingdeforming characteristics, as noted above. Therefore, though some ofthese processes have been described with respect to the blank 30, theinstruments 12 may be described in similar manners.

Coating, sandblasting, etching, anodizing, ion implantation orelectro-polishing, as noted above, may be used to modify the surfaceproperties of the instruments 12 or blanks 30. For example, amicro-abrasive sandblasting device disclosed in U.S. Pat. No. 6,347,984may be a suitable device for treating endodontic instruments 12 of thepresent invention, the content of which is incorporated herein byreference. Another suitable device may be one disclosed in U.S. Pat. No.5,941,702, the content of which is also incorporated herein byreference. This exemplary device disclosed is a dental air-abrading tooltypically used for etching hard surfaces to enhance bond strength ofadhesives, which includes a solid body having internally reamedpassageways through which a gaseous fluid and an abrasive material arecarried. A connector is mounted on one end of the body for connectingone of the body's internal passageways to a supply of gaseous fluid anda nozzle is mounted on the other end of the body for directing thegaseous fluid to a surface. A supply of an abrasive material is coupledto another internal passageway of the body. The nozzle includes aninternal mixing chamber for mixing the gaseous fluid and abrasivematerial entering therein from the body's internal passageways. Someslight modifications may be made to adapt it for use in the presentinvention

Other physical alterations of the surface such as burnishing, may alsoresult in a surface layer with reduced excess oxides.

Other exemplary treatment methods may be found in U.S. Pat. Nos.6,605,539, 6,314,743, 5,775,910, and 5,393,362, the contents of all ofwhich are hereby incorporated by reference.

Chemical etching may also be used and may be carried out in any knownprocess, including nitric acid passivation.

Ion implantation is another method that may be used, to impart changesto either small or large regions of the surface of the blank 30, forexample, to generate an amorphous surface, which may lead to increasedsurface hardness, reduced surface friction coefficient, increased wearresistance, reduced surface wetting behavior, and even an enhancement inpassivation, if desired. Ions useful for implantation may includeoxygen, nitrogen, carbon, boron, cobalt. Process conditions during ionimplantation may also be controlled to minimize hydrogen embrittlement.

These surface treatment processes may be performed either on the blank30 or the instrument 12, as noted above. When performed on the blank 30,the modification may be present on portions of the instrument 12 thathave not been ground, for example, the proximal portion 16 a of thenon-working shank 16, if desired, and/or portions of the peripheralsurfaces and/or cutting edges 18 of the working portion 22.

Surface modification such as roughening made by sandblasting, orchemical modification made by chemical etching, anodizing or ionimplantation, on the proximal end 16 a of the non-working shank 16 mayaid in the attachment of the shank 16 to a handle 25, as shown in FIGS.7, 7 a and 7 b. The handle 25 may be attached by crimping, by anadhesive, or combinations thereof.

Such surface modification on the proximal end of the non-working shank16 either macroscopically or microscopically, depending on thetreatment, may result in the increase of the attachment strength of theshank 16 to the handle 25, decreasing the chances of separation betweenthe handle 25 and the instrument 12 during operation, as discussedfurther. When the modification is performed on the instrument 12 afterthe instrument 12 has been formed, the coating, sandblasting, anodizing,ion implantation, etching or electro-polishing process may be performedon the entire instrument 12 or on selected portions of the instruments12, to modify the entire instrument 12 or only the desired portion orportions. The process may also remove any burrs or irregularitiesgenerated during the manufacturing process while creating a modifiedsurface structure at the same time.

Coating, sandblasting, anodizing, ion implantation, etching orelectro-polishing may also modify the working surfaces 18, whetherperformed on the blank 30 or the instrument 12. When performed on theblank 30, the treated areas may be the working surfaces 18 that are partof the original blank 30, i.e., the working surfaces 18 having the samecircumferential span or diameter as the starting blank 30. Additionaltreatment may also be performed on portions of the instrument 12 aftergrinding, if desired. In other words, the treatment processes may berepeated.

Some treatment methods may also impart a different color to the treatedportions. These colored portions may serve as length, depth or wearindicator, as discussed further below.

In addition, other chemical surface treatments for the blank 30 may beemployed including coatings for friction reduction and/or durability.Some of these coating may include titanium nitride coating, tungstencarbide coatings, diamond-like carbon coatings, chromium coating,calcium immersion, and others for maintaining and improving thesharpness of the working surfaces 18 and to minimize the built up ofoxide layers, as noted above. The formation of titanium nitride on apassivated surface was reported to enhance the barrier to further Ni2+ion migration, as noted in an article by L. Tan, W. C. Crone/ActaMaterialia 50 (2002) 4449-4460, the content of which is herebyincorporated by reference.

In one embodiment, for a coated or treated blank 30, the coating ortreated surface may be of a color different form the blank 30 itself.This color may remain on the un-ground portion. For the working portion22, the un-ground portion may serve as a depth or length indicator.

During a grinding process, a fixed grinding and turning speed may resultin, for example, helical cutting edges 18 being formed at regularintervals along the working portion 22. As the edges 18 may be of thesame circumferential span as the blank 30, these edges may not haveundergone any grinding. The un-ground edges 18 would thus have adifferent color as the ground portions. When the edges 18 appear atregular intervals, such colored intervals may be useful in indicatingthe length or depth of the file inside a canal during use. For example,the first cutting edge 18 following the pilot portion 10 may beindicated as 1, with a corresponding correlation table for indicatingthe distance from the tip of the pilot portion 10, either to thebeginning and/or the end of the edge 18, as the edge 18 is slanted. Suchcolored blanks 30 may also serve to indicate the wear characteristics ofthe instrument.

Similarly, when the coating or treatment is carried out on the cuttingsurfaces 18 of the instrument 12, the color may likewise serve as alength, depth or wear indicator.

Further, a treatment process having a sequence of first reducing theoxide layer prior to drawing, then add treatments such aselectro-polishing, anodizing, coatings including various coatingsmentioned before, and drawing again, may be used either on the blank 30or on the instrument 12.

The present invention also relates to the manufacture of a set ofendodontic instruments 12 having varying maximum circumferential spans,for example, diameters. In one embodiment, one blank 30 having acircumferential span is made into one instrument 12 in the set and thecircumferential span of the blank 30 corresponds to the maximumcircumferential span of the working portion 22, and/or the proximal endof the instrument 12, such as shown in FIGS. 8 a-8 c. Each of theinstrument 12 shown in FIG. 8 a includes forming a working portion 22including at least one working surface 18 having a circumferential span,said working portion 22 extending not more than the length of thenon-working shank 16 and having a maximum circumferential spansubstantially corresponding to the circumferential span of therespectively blank 30. In the exemplary embodiment as shown in FIG. 8 a,the working portion 22 has a substantially circular cross-section, andat least two spiral or helical working surfaces 18, as is also shown inFIG. 2. In other embodiments, working surfaces 18 may haveconfigurations like those exemplified in FIGS. 2 a, 3, 3 a, 3 b, 4, 4 a,4 b, 4 c, 4 d, 4 e and 4 f, discussed above.

The number of instruments 12 in a set may vary, for example, from as fewas three instruments 12 in the set, though typically more than three ina set, and more typically more than 6 in a set, all having differentcircumferential spans. In general, the dental professional starts withthe one having the smallest circumferential span and progressively movesto larger and larger ones, until the root canal is fully cleaned andprepared for filling.

As shown in FIG. 8 a, each of the non-working shank 16 is ground to havea diameter that is substantially smaller than the diameter of the blank30, each shank portion 16 having a different diameter from the others inthe series.

In another embodiment, a set of instruments 12 are made from a set ofblanks 30 having an identical circumferential span. Each blank 30 may beground to generate a non-working shank 16 having a proximal end 16 a, adistal end 16 b, and at least a portion having a substantially smallercircumferential span than that of the blank 30. In one embodiment, onlyone instrument in the set may have a working portion 22 having a maximumcircumferential span substantially corresponds to the circumferentialspan of the blank 30 and a portion of the shank portion 16 of each ofthe instruments 12 in the set may be of substantially the samecircumferential span, which is smaller than the circumferential span ofthe blank 30. In another embodiment, only one instrument 12 in the setmay have at least a portion of the shank portion 16 that is of thesubstantially the same circumferential span as that of the blank 30, andall the other ones have smaller circumferential span than the blank 30.

The pilot portion 10 is formed near one end close to the working portion22 of each instrument 12, as described above. The proximal end 16 of thenon-working shank 16 may be adapted to be attached to a handle 25, isshown in FIGS. 7, 7 a and 7 b. The distal end 16 b is adjacent to theworking portion 22, which may have a configuration similar to thosediscussed in FIGS. 2, 2 a, 3, 3 a, 3 b, 4, 4 a, 4 b, 4 c, 4 d, 4 e and 4f. The pilot portion 10 and the non-working shank 16 may also have anyof the configurations disclosed previously.

Only three instruments 12 are shown here in the example. In practice, asmany instruments 12 having a working portion with different maximumcircumferential span or diameter as is desired by a practitioner may bemanufactured.

These instruments 12 may also undergo treatment using any of thetreatment methods disclosed above, including coating, sandblasting,anodizing, ion implantation, electro-polishing, etching, heat setting,cryogenic treatment, or combinations thereof, for modifying the workingportion 22, and/or the shank 16, and/or the pilot portion 10. In anotheraspect, the set of blanks 30 used may be subjected to the sametreatments or combinations thereof.

The blanks 30 may also be treated prior to the grinding process, asnoted above. In one aspect, the blank 30 may be treated at itsmanufacturing stage. In another aspect, the blank 30 may be treatedafter the manufacturing process, but before the grinding process.

According to another embodiment of the invention, the method formanufacturing a set of endodontic instruments 12 may include providing aset of groups of blanks 30, each group having at least two blanks 30,and the number of groups are of a smaller number than the number ofinstruments 12 in the set, wherein each blank 30 includes acircumferential span, and each group having a different circumferentialspan from another group.

The working portion 22 including a working surface 18 and acircumferential span, may extend no more than the length of thenon-working shank 16. The configuration of the working surfaces 18, thepilot portion 10, and the non-working shank 16, may be as shown in FIG.2, or may be similar to those shown in FIGS. 2 a, 3, 3 a, 3 b, 4, 4 a, 4b, 4 c, 4 d, 4 e and 4 f, discussed above.

Although more than one instrument 12 may be made from blanks having thesame circumferential span, for example, diameter, only one instrument 12in a set made from each group of blanks 30 may have a working surfacehaving a maximum circumferential span substantially corresponding to thecircumferential span of each group of blanks 30, such as exemplified inFIG. 8 b. FIG. 8 b shows a series of three instruments 12 in a set madefrom blanks 30 having the same circumferential span or diameter. In oneembodiment, at least one of the instruments 12 in a set made from thesame group of blanks 30 may have at least a portion towards the proximalend 16 a of the shank portion 16 having substantially the samecircumferential span as that of the blank 30, as exemplified here inFIG. 8 b. In other embodiments, the entire length of the shank 16 may beground to be of one uniform circumferential span, the same in all threeinstruments 12, as shown in FIG. 8 c. This process has the advantage ofstocking fewer sizes of starting blanks 30 than the above process ofmaking each instrument 12 having a different maximum circumferentialspan out of a respective blank 30 having a circumferential span similarto the maximum circumferential span of the working portion 22, althoughthe process described earlier has the advantage of not having to removemore material from the blank in order to make an instrument 12 having asmaller circumferential span than the circumferential span of thestarting blank 30, saving material and process cost.

As mentioned before, in one embodiment, a series of two instruments 12in a set may be made from one group of blanks 30 having identicalcircumferential span even though only one of the instruments 12 in theset may have a working portion 22 having the same circumferential spanas the blank 30. In another embodiment, a series of three instruments 12in a set may be made from a group of blanks 30 having an identicalcircumferential span even though only one of the instruments 12 in theset may have a working portion 22 having the same circumferential spanas that of the blank 30. In other embodiments, more than threeinstruments 12 in a set may be made from a group of blanks 30 havingidentical circumferential span even though only one of the instruments12 in the set may have a working portion 22 having the samecircumferential span as that of the blank 30.

In one aspect, at least a portion of each of the instruments 12including the shank 16, the working portion 22, the pilot portion 10 orcombinations thereof may be treated, as noted above.

In another aspect, a set of blanks 30 having undergone coating,sandblasting, anodizing, ion implantation, etching, heat setting,cryogenic treatment, electro-polishing or combinations thereof may beused.

In one embodiment, the instrument 12 in each set may also have a handle25 at its distal end for manual manipulation. In another embodiment,instrument 12 in each set may have a handle 25 at its distal end that isadapted for attachment to a mechanical handpiece. These are similar tothose exemplified in FIGS. 7, 7 a, 7 b, except now in sets. A mechanicalhandpiece may be a rotary handpiece or a vibratory handpiece.

When adapted for rotation by means of a mechanical handpiece, the speedof rotation may be at any conventional level up to a level of about 400to about 1,000 rpm. This is possible because of the short workingportion 22 and smaller areas of contact between the working surfaces 18and the canal walls. This is an improvement over the traditionalinstruments having a working portion along almost the entire length ofthe instrument.

Any of the surface treatments may also improve the strength ofattachment between the handle 25 and the proximal end 16 a of theinstrument 12, as noted above. The surface treatment may tend to roughenthe surfaces to increase the area of contact, either macroscopically ormicroscopically, depending on the treatment. This improvement alsoenables the instrument 12 to be rotated at the higher speeds with lowerincidences of detachment between the instrument 12 and the handle 25.

When the attachment strength between the handle 25 and the instrument 12is increased, any breakage, if any, may be more likely to occur at anyweak points generated by the grinding process, rather than theseparation between the handle 25 and the proximal end 16 a of theinstrument 12. To increase the likelihood that such breakage may occurtowards the proximal end 16 a of the shank portion 16, rather than atthe transition between the working portion 22 and the distal end of theshank 16 b, for the instruments 12 with a shank 16 having smallcircumferential span or diameter, the shank 16 may be tapered, such asexemplified in FIG. 9, so that the weak point may be more likely to betowards the thinner proximal end 16 a of the shank 16, and any brokenparts of the instrument 12, if lodged in the canal, may be more easilyremoved.

In another aspect, such as shown in FIG. 9, the proximal end 16 a of theshank 16 has a smaller diameter than the distal end 16 b and thetransition between the distal end 16 b of the shank 16 and that distalend 24 of the working portion 22 is gradual and smooth, reducing orminimizing any stress that may be created by the grinding process.

In a further aspect, if desired, the shank 16 may be ground to have aportion 16 c having a reduced circumferential span or diameter, as shownin FIG. 9 a. The reduced diameter portion 16 c may take the shape of agroove (U-shaped) or a notch (V-shaped). This reduced diameter portion16 c provides a predictable break point, in case the instrument 12encounters some blockage in the canal that may impede its progress sothat the instrument 12 may break at the reduced diameter portion 16 cfor easier retrieval from the tooth. This reduces the chance of having abroken piece of an instrument lodged deep within the canal of the tooth.In addition to serving as a predetermined weakness point, the reduceddiameter portion 16 c may also be adjusted to serve as a depth of cutindicator.

Any surface treatments on the working portion 22 may also lead to bettercutting efficiency. This may also lower the degree of discomfort for thepatient.

As noted above, a blank can be a spool or can be a single piece.

The pilot portion 10 and/or the working portion 22 may be formed bygrinding, as exemplified above, they may also be formed by molding orcasting.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention.

1. A method for manufacturing an endodontic instrument comprising:providing a blank for making an instrument, said blank having acircumferential span; grinding said blank to form a non-working shankportion having a proximal end and a distal end, at least a portion ofthe shank having a substantially smaller circumferential span than thatof the blank; forming a working portion extending not more than thelength of the non-working shank on said blank adjacent the distal end ofthe non-working shank, and having a maximum circumferential spansubstantially corresponding to the circumferential span of the blank;forming a pilot portion near one end of the blank close to the workingportion; treating at least a portion of the instrument comprising atleast a portion of the shank portion, the working portion, the pilotportion or combinations thereof; and attaching at least a portion of thetreated shank portion to a handle portion.
 2. The method of claim 1wherein said pilot portion comprises a non-cutting portion, abrasivesurfaces, or a continuous extension of the working portion.
 3. Themethod of claim 1 further comprises flattening at least a part of theworking portion.
 4. The method of claim 1 wherein said treating theshank portion comprises roughening the surface.
 5. The method of claim 1wherein said treating comprises coating, sandblasting, anodizing, ionimplantation, electro-polishing, etching, heat setting, cryogenictreatment or combinations thereof.
 6. The method of claim 4 furthercomprises attaching said roughened portion to a handle.
 7. The method ofclaim 1 wherein said treating is done prior to grinding or during themanufacturing of the blank.
 8. The method of claim 1 wherein saidworking portion has a longitudinal axis and comprises at least onehelical working surface; edges forming a continuous curve; edgestwisting not more than 359° about the longitudinal axis; curved cuttingedges about the longitudinal axis; straight cutting edges along thelongitudinal axis; straight cutting edges at an oblique angle of thelongitudinal axis; projections that are non-intersecting; orcombinations thereof.
 9. The method of claim 1 wherein said treatingimparts a different color onto the treated surfaces.
 10. A method formanufacturing a set of an endodontic instruments comprising: providing aset of blanks, said blanks having varying circumferential spans;grinding each of said blank to form a non-working shank portion having alength, a proximal end, and a distal end, wherein at least a portion ofsaid shank portion having a substantially smaller circumferential spanthan that of the blank; forming a working portion on each blank adjacentto the distal end of said shank portion and extending not more than thelength of the non-working shank, said working portion having a maximumcircumferential span substantially corresponding to the circumferentialspan of the blank; and forming a pilot portion near one end of theinstrument close to the working portion.
 11. The method of claim 10wherein said pilot portion comprises a non-cutting portion, abrasivesurfaces, or a continuous extension of the working portion.
 12. Themethod of claim 10 further comprising treating at least a portion ofeach of the instruments comprising at least a portion of the shank, theworking portion, the pilot portion or combinations thereof.
 13. Themethod of claim 12 wherein said treating comprises coating,sandblasting, anodizing, ion implantation, electro-polishing, etching,heat setting, cryogenic treatment, or combinations thereof.
 14. Themethod of claim 12 wherein said treating is performed prior to thegrinding process, or during the manufacturing of the blank.
 15. Themethod of claim 10 further comprises flattening at least a part of theworking portion.
 16. A method for manufacturing a set of endodonticinstruments comprising: providing a set of groups of blanks, the set andgroups each having a finite number of blanks, wherein each group havinga different circumferential span from another group; grinding each blankto generate a non-working shank portion having a length, a proximal endand a distal end, each instrument made from the same group of blanks hasat least a portion towards the distal end having a substantially smallercircumferential span than that of the blank; forming a working portionhaving cutting edges and a circumferential span adjacent said shankportion, said working portion extending not more than the length of thenon-working shank portion; forming a pilot portion adjacent the workingportion; wherein only one instrument in the set made from each group ofblanks has a maximum circumferential span substantially corresponding tothe circumferential span of each group of blanks.
 17. The method ofclaim 16 wherein at least one of said instruments in the set made fromthe same group of blanks has at least a portion towards the proximal endhaving substantially the same circumferential span as that of the blank.18. The method of claim 16 wherein the working portion has alongitudinal axis and comprises at least one helical working surface;edges forming a continuous curve; edges twisting not more than 359°about the longitudinal axis; curved cutting edges about the longitudinalaxis; straight cutting edges along the longitudinal axis; straightcutting edges at an oblique angle from the longitudinal axis;projections that are non-intersecting; or combinations thereof.
 19. Themethod of claim 16 further comprises treating at least a portion of eachof the instruments including the shank, the working portion, the pilotportion or combinations thereof.
 20. The method of claim 19 wherein saidtreating comprises coating, sandblasting, anodizing, ion implantation,electro-polishing, etching, heat setting, cryogenic treatment orcombinations thereof.
 21. The method of claim 19 wherein said treatingcomprises roughening the proximal end of the shank portion.
 22. Themethod of claim 19 wherein said treating is performed during themanufacturing of the blank.
 23. The method of claim 16 wherein the pilotportion comprises a non-cutting portion, abrasive surfaces orcombinations thereof.
 24. The method of claim 16 wherein each group hasat least two blanks.
 25. The method of claim 21 further comprisesattaching said roughened portion to a handle.
 26. The instrument ofclaim 19 wherein said treated portions have a different color from theuntreated portions.